1. Field of the Invention
This invention relates to electrical cabling and, more particularly, to an electrical cable having a tie layer disposed between a first layer and a second layer and a method for manufacturing same.
2. Description of Related Art
Many electrical cables, such as seismic, oceanographic, and wireline cables, are sometimes used in corrosive environments at pressures that may range from atmospheric to very high and at temperatures that may range from arctic to very high. Accordingly, the insulating and jacketing materials used in such cables must be able to withstand these harsh environments, as well as have the dielectric and capacitive properties desirable for the cables. Polymers belonging to the polyolefin family, such as polyethylene, polypropylene, and polyethylene propylene co-polymer, and polymers belonging to the fluoropolymer family, such as ethylene tetrafluoroethylene, fluorinated ethylene propylene, polytetrafluoroethylene/perfluoromethylvinylether co-polymer, and perfluoroalkoxy polymer, are commonly used as insulating materials in these cables.
It is often desirable to have multiple layers of insulating and jacketing materials surrounding the conductors in seismic, oceanographic, and other electrical cables so that the cable will have the desired electrical properties and be able to withstand the environment in which it is used. Generally, it is also desirable to bond or “pot” the insulating layers to a connector or the like within a cable termination to inhibit moisture or other contaminants from penetrating between the insulating layers and/or from entering the connector. Polyolefin and fluoropolymer materials, however, may not bond well to conventional epoxy, nitrile, ester, or urethane-based potting compounds. In general, only cyanoacrylate adhesives are effective in bonding these materials in electrical cable applications. Cyanoacrylate adhesives, however, may be brittle and may be unable to withstand the pressure and/or temperature cycling encountered by such cables.
Primers have been used to enhance the bonding, but they are not as effective on polyolefin and fluoropolymer materials as on other polymeric materials. Surface treatments, such as flame treatment, corona discharge, and solvent etching, have been used to enhance the bonding characteristics of polyolefin and fluoropolymer materials. These techniques, however, may be time consuming and impractical in certain situations. For example, it may be difficult to apply these treatments to large numbers of small, insulated conductors that are bundled together. As a result, such surface treatments may provide results that are less than optimal.
Multiple layers of different potting materials have also been used to overcome the bonding problems of polyolefin and fluoropolymer materials. However, this process has proven to be difficult and time consuming. In some situations the layers of potting material may not effectively bond together, which provides the potential for moisture ingression. Further, a longer length cable termination results from this process, which is generally undesirable.
When the insulating layer and the jacketing layer are not properly bonded together, such as in a cable having a polyvinylchloride insulating layer with a nylon jacketing layer, a small, often microscopic void or voids may exist between the insulating layer and the jacketing layer, which may allow wicking of fluids therein. Moreover, mechanical flexing of such layers having a void or voids therebetween may cause wrinkling and separation of the layers, inhibiting the usefulness of the cable.
Some conventional electrical cables have utilized insulating and jacketing materials that have better bonding characteristics than polyolefin and fluoropolymer materials, such as nylon and thermoplastic polyester elastomers (e.g., Hytrel®, manufactured by E. I. du Pont de Nemours and Company of Wilmington, Del., U.S.A.). However, such materials generally have electrical properties that are inferior to polyolefin materials.
The present invention is directed to overcoming, or at least reducing, the effects of one or more of the problems set forth above.